Heart failure (HF) afflicted 6.5 million Americans in 2017, carries 5-year mortality of ~50%, and will likely increase to > 8 million by 2030. The lack of significant improvement in mortality for the last 46 years, the reality of needing to discontinue effective medications due to hypotension in heart failure with reduced ejection fraction (HFrEF), and the paucity of effective treatment for heart failure with preserved ejection fraction (HFpEF) combine to suggest that new treatments are needed. Cardiac myosin binding protein-C (cMyBPC) resides on the thick filament of the heart muscle. Phosphorylation of cMyBPC at its M-domain increases cross-bridge cycling rate. Because increasing cross-bridge cycling rate can improve both contractility and lusitropy, we hypothesize that phosphorylation of cMyBPC provides a novel central mechanism that can prevent and treat HF due to different causes. Using mouse models that mimic de-phosphorylated and phosphorylated cMyBPC at 3 serine (S) sites in the M-domain, we recently discover that cMyBPC phosphorylation mitigates both aged-related development of HFpEF and trans-aortic constriction (TAC) surgery induced HFrEF, as seen by improved survival and better preservation of diastolic function. Thus, cMyBPC phosphorylation holds potential to treat both HFrEF and HFpEF. However, we find evidence that 2 new S phosphorylation sites outside our study of 3 S sites add significant functional effects. Consequently, we have made 2 new knock-in mouse models to include the new sites for elucidating the effects of maximally phosphorylated cMyBPC(5SD) and dephosphorylated cMyBPC(5SA) M-domain. We also find evidence that pressure stress can activate focal adhesion kinase (FAK) to phosphorylate tyrosine (Y) residue(s) in cMyBPC. This discovery leads to a new supporting hypothesis that pressure stress triggers FAK to phosphorylate cMyBPC to increase contractility as a compensatory response. With these discoveries in mind, we intend to determine the efficacy of maximal M-domain phosphorylation and elucidate the novel FAK-cMyBPC mechanism. Aim #1: Determine the efficacy and companion mechanisms of phosphorylated cMyBPC to preserve cardiac function under HF inducing conditions of aging, pressure stress, and obesity. We will challenge mice with 2-yr aging, TAC, or high fat diet. We will use a combination of functional and biochemistry techniques to determine the underlying mechanisms. Ability of cMyBPC(5SD) mouse to resist deterioration and effectiveness of using cMyBPC(5SD) gene therapy to reverse failing WT hearts will quantify the efficacy of cMyBPC phosphorylation for prevention and treatment respectively. Aim #2: Elucidate signaling mechanism and functional results of pressure stress induced tyrosine phosphorylation of cMyBPC. We will identify Y site(s), confirm FAK-cMyBPC interaction, and elucidate effects of FAK phosphorylating cMyBPC on models ranging from intact papillary muscle to new knock-in mouse. Impact: Efficacy results and mechanistic insights stemming from this study provide evidence for translating cMyBPC phosphorylation to new HF treatment.